An LDV scanning head is proposed based on a pair of rotating optical wedges. Modelling demonstrates how the wedges can be configured to scan point-by-point, in a line and in a circle. The circular scan is considered for the tracking application and shown to offer certain advantages over alternative systems based on dual mirrors and a Dove prism in terms of lower apparent velocities at key rotation orders.

Vibrometry is a modern contactless measurement technique to analyze vibrations in different applications. It is extremely important for industry and research. Since spatial light modulators (SLM) have been developed, new techniques in vibrometry are possible. This paper presents two applications which use the SLM as actor instead of a galvanic mirror. Both techniques modify the phase of the wave front of a laser beam by using an SLM. On the one hand, it allows varying the focus plane and repositioning of a spot without any mechanical device. For that, special patterns have to be written to the SLM. On the other hand, overlay patterns can be used to reduce speckle drop-outs nearly without changing position and focus of the spot. For both applications an optimized signal level is the key to get sufficient results in a rougher environment.

In a previous work[1], the authors presented preliminary data showing how noise can be mapped as a function of beam focus and standoff distance. This analysis builds on the previous work, but presents a method of mapping laser Dopopler vibrometer (LDV) noise which can be broadly generalized. The apparatus used in the experiments is a Polytec OFV505 with a custom servo-actuated attachment to the focus ring, which is mounted to linear positioning stages to control standoff distance and dither location.
A high resolution grid of measurement locations is generated to create a map of signal strength as a function of both standoff distance and "focus error" - a description of the degree to which the beam is defocused, expressed in terms of how the standoff would need to be adjusted in order to move the beam into focus. Using this approach, the particular optics of the LDV system are no longer directly a factor, as determining the relationship between the focus adjustment and standoff distance should be possible with any system. Further noise maps from experiments which dither the horizontal location of the measurement beam show how the signal field can change for nearby measurement locations on a rough surface and highlight the importance of averaging LDV measurements.

One of the most important parts of a fiber-laser vibrometer is demodulation electronic section. The distortion, nonlinearity, offset and added noise of measured signal come from electronic circuits and they have direct influence on finale measuring results. Two main parameters of an investigated vibrating object: velocity V(t) and displacement s(t), influence of detected beat signals. They are: the Doppler frequency deviation f(t) and phase shift φ(t), respectively. Because of wide range of deviations it is difficult to use just one demodulator. That is the reason why we use three different types of demodulators. The first one is the IQ demodulator, which is the most sensitive one and its output is proportional to the displacement. Each IQ channel is sampled simultaneously by an analog to digital converter (ADC) integrated in a digital signal processor (DSP). The output signals from the two FM
demodulators are proportional to the frequency deviation of heterodyne signals. They are sensitive directly to the velocity of the object. The main disadvantage of scattered light interferometry
system is a “speckle effect”, appearing in relatively large amplitude fluctuation of a heterodyne signal. To minimize “speckle effect” influence on quality of beat signals we applied the automatic gain control (AGC) system.
Data acquisition, further signal processing (e.g. vibration frequency spectra) and presentation of results is realized by PC via USB interface.

The presentation will outline the motivation, results and experience of the development and application of a Universal Tip Timing Calibrator (UTTC) by the Siemens Tip Timing expert group. Due to the importance of the Tip Timing blade vibration measurement technology for the development of new gas turbine frames it is indispensible to calibrate these systems to international traceable standards. The very complex matter of tip timing signals does not allow to refer to simple physical and easy available laboratory standards in a standard working procedure. Even very sophisticated and expensive arbitrary wave and pattern generators are not able to generate signals to be used as calibration signals for multi-sensor tip timing systems of the last generation. So far, these 3rd and 4th
generation Blade Vibration Tip Timing Measurement (BVTTM) systems could not be tested and calibrated completely within their dedicated application range regarding blade vibration amplitude, frequency and dynamic response.
Based on this situation, the Siemens Tip Timing expert community decided the development of a universal and wide range application Tip Timing Simulator and Calibrator four years ago. Meanwhile, this device exists and is widely used for BVTTM system development, field system set up, data validation and off-line data evaluation.
Inside the paper, the technical features and the software capabilities as well will be described in detail. Finally, two application examples with two different BVTTM systems are presented and the results are being discussed.
As a summary it can be expressed, that the UTTC was found as a very helpful instrument for an optimal Tip Timing system setup.

Performances of blade tip timing measurement systems (BTT), recently used for non contact turbine blade vibration measurements, in terms of uncertainty and resolution are strongly affected by sensor
characteristics. The sensors used for BTT generate pulses, to be used also for precise measurements of turbine blades time of arrival. All the literature on this measurement techniques do not address this problem in a clear way, defining the relevant dynamic and static sensor
characteristics, fundamental for this application. Till now proximity sensors used are based on optical, capacitive, eddy current and microwave
measuring principle. Also pressure
sensors has been used.
In this paper a new sensing principle is proposed. A proximity sensor based on magnetoresistive sensing element has been assembled end tested. A simple and portable test bench with variable speed, blade tip width, variable clearance was built and used in order to characterize the main sensor performances.

DHMs have unique features especially relevant for MEMS characterization. They provide 3D topography for large vertical ranges with interferometric resolution, in a single acquisition, without any lateral or vertical scanning. Any standard microscopic objective can be mounted on them, including those with correction for cover glass thickness. In this paper, DHM is operated in conjunction with a laser pulsed stroboscopic module providing synchronization of camera acquisition and shutter, laser pulses with length down to 7.5 ns, and MEMS excitation signal up to 25 MHz. These systems can measure fast movements over large vertical amplitude, in-and out-of-plane motions of device with complex geometry, provide a statistical analysis of multiple single devices, and can measure under vacuum or in liquid and/or through transparent window. This is illustrated with the presentation of the measurements of a cantilever, an ultrasonic transducer, a variable capacitor, and a gyroscope.

One challenging application field of optical vibrometry is micro-and nanometrology. Since small structures
resonate at high frequencies and with small vibration amplitudes this application area requires high spatial resolutions, high amplitude resolutions, and high measurement bandwidths. In addition, small structures are sensitive to heating because even a small heating energy can raise temperatures dramatically. Laser-Doppler technique provides amplitude resolutions down to the range of a few
, but for some applications even lower resolutions are required. In this paper, I summarize interferometric measurement solutions from basic physics science branches where amplitude-noise levels in the attometer regime have been demonstrated empirically and I discuss if these resolutions can be transferred to industrial applications. In addition, I propose heterodyne
interferometry for the broad bandwidth measurements of the electrical field vector of light and I derive the theoretic resolution limit for in-plane-vibration measurements for a new detection method for the first time.

The paper presents novel interferometric measurement technique applied for MEMS dynamic properties measurements. The method was developed especially for multi-channel interferometer developed under SMARTIEHS EU project. The method employs sinusoidal modulation of light and novel smart-pixel camera detector. The measurement results obtained with developed measurement system and commercial Polytec system, obtained while measuring reference objects, are in good correspondence showing usefulness of proposed method.

In the paper we present the idea and measurement results of a modified laser interferometer with improved measurement linearity and measurement resolution. Presented solutions allow for linearity increase below 1nm mark with measurement resolution even of single picometers (depending on the noise parameters of the laser source and detection electronics) in the basic heterodyne configuration of the optical elements.

Today's commercial solutions for vibration measurement and modal analysis are 3D-scanning laser doppler vibrometers, mainly used for open surfaces in the automotive and aerospace industries and the classic three-axial accelerometers in civil engineering, for most industrial applications in manufacturing environments, and particularly for partially closed structures.
This paper presents a novel measurement approach using a single laser beam
device and optical reflectors to simultaneously perform 3D-dynamic measurement as well as geometry measurement of the investigated object. We show the application of this so called laser tracker for modal testing of structures on a mechanical manufacturing shop floor. A holistic measurement method is developed containing manual reflector placement, semi-automated geometric modeling of investigated objects and fully automated vibration measurement up to 1000 Hz and down to few microns amplitude. Additionally the fast set up dynamic measurement of moving objects using a tracking technique is presented that only uses the device's own functionalities and does neither require a predefined moving path of the target nor an electronic synchronization to the moving object.

Laser-Doppler vibrometry (LDV) is a proven technique for vibration analysis of mechanical structures. A wavelength of 633 nm is usually employed because of the availability of the relatively inexpensive Helium-Neon laser source which has a good coherence behavior. However, coherence break-down through the beat of multiple longitudinal modes and the limited detector carrier-to-noise-ratio (CNR) at a measurement laser power of 1 mW have prevented a wide use of LDV in remote sensing applications. Such applications in civil engineering are bridges, towers or wind turbines. The lower photon energy of IR light at 1550 nm wavelength increases the CNR by a factor 2.4. This helps especially in the condition where the carrier power decreases below the FM threshold. We have designed a heterodyne
interferometer which allows the shot noise limited detection at 1550 nm wavelength close to the theoretical possible CNR. We present calculations of the fundamental noise contributions in interferometric light detection for a comparison of the achievable CNR between common HeNe vibrometers and IR vibrometers. The calculations are backed by measurements that show the devices working close to the theoretical limits. The achievable noise level of the demodulated velocity signal is shown in dependence from the standoff distance. Our novel heterodyne
interferometer has been transferred to the Polytec product RSV-150. An application example of this new sensor will be demonstrated.

An adaptive algorithm has been designed to treat interferometric self-mixing signals for weak and moderate laser feedback. With regard to the creation of an embedded displacement sensor, the reconstruction process is inspired from the interpolation feature found in digital-to-analog converters. By using an adaptive filter as the central process, the algorithm presents a high potential of parallelism to meet timing restrictions. A validation for different signal scenarios was carried out. The obtained precision and ease of maintainability enlightens its capabilities to be coupled with other signal processing methods to produce better system reliability.

An optical feedback
interferometer has been used as a sensor for measuring the deformation of the beams under dynamic loading. The compactness, non-contact nature, high accuracy (below half wavelength of the laser) and the cost-effectiveness of this sensor makes it a suitable choice for material deformation measurements. A general procedure of the measurement is described in detail, including the proposed solution to deal with the speckle effect which appears when large deformations are presented. The performance of the proposed sensor has been compared and validated with a commercial contact LVDT sensor showing measurement differences below 20μm (2.9%).

In this paper, we present a self-mixing double-head laser diode velocimeter. Analyzes are performed to evaluate the sensitivity to misalignment for this setup and calculate errors due to this misalignment. The analyses and calculations are verified by experimental results.

In this paper, we present a real-time implementation of a Self-Mixing (SM) interferometric laser diode
(LD) based vibration sensor coupled with an embedded MEMS
(microelectromechanical system) accelerometer. Such a sensor allows measuring correct target movements even when the LD based SM sensor is subject to extraneous movements. This results in a vibration sensing system that can be used for embedded applications as there is no more need of keeping the sensor stationary. Such an approach opens the way for the use of such laser sensors in conditions where the use of anti-vibration support is not available or possible. The proposed data fusion between a MEMS accelerometer and a LD based SM sensor results in a robust, compact and low-cost sensing system.

Effect analysis of external optical feedback on waveform and spectrum of semiconductor laser autodyne signal has been performed. The method of nanovibration amplitude determination has been described. The method involves measuring ratio of the first spectral components of nanovibration autodyne signal to one of the additional mechanical vibrations, taking into account the level of external optical feedback. It has been experimentally shown, that taking into account external optical feedback can significantly improve the accuracy of nanovibration measurements.